Communication devices such as wireless devices are also known as e.g. User Equipments (UE), mobile terminals, terminals, wireless terminals and/or mobile stations. Terminals may be enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which may be divided into cell areas, wherein each cell area may be served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “Enhanced Node-B (eNodeB or eNB), “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the DL and Discrete Fourier Transform (DFT)-spread OFDM in the UL. The basic LTE DL physical resource may thus be seen as a time-frequency grid as illustrated in FIG. 1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. One resource element comprises one OFDM symbol including a cyclic prefix.
Machine-Type Communication (MTC)
Machine Type Communication (MTC) is a form of data communication which involves one or more entities that do not necessarily need human interaction. MTC devices are devices which communicate through MTC. In some particular instances, MTC devices may be wireless devices equipped for MTC, as just described, which wireless devices may communicate through a Public Land Mobile Network (PLMN) with MTC Server(s) and/or other MTC Device(s). An MTC Server is a server which may communicate to the PLMN itself, and to MTC Devices through the PLMN. The MTC Server may also have an interface which may be accessed by the MTC User. The MTC Server may perform services for the MTC User. An MTC User may use the service provided by the MTC Server. MTC devices may be, for example, home and/or building automation devices, alarms, emission control, toll payment devices, people tracking devices, parcel tracking devices, sensor networks, industrial automation devices, personal network devices etc . . . .
It is efficient for MTC operators to be able to serve MTC UEs using already deployed radio access technology. Therefore, 3GPP LTE has been investigated as a competitive radio access technology for efficient support of MTC. Lowering the cost of MTC UEs is an important enabler for implementation of the concept of the “internet of things”. MTC UEs used for many applications may require low operational power consumption and are expected to communicate with infrequent small burst transmissions. In addition, there is a substantial market for the M2M use cases of devices deployed deep inside buildings which may require coverage enhancement, in comparison to the defined LTE cell coverage footprint.
Enhanced coverage may be understood as coverage improvement in comparison to defined LTE cell coverage footprint as engineered for “normal” LTE UEs. A “normal” LTE UE may be understood as an LTE UE which has at least the default implementation, including: (a) being able to transmit and receive over the full system bandwidth; (b) having at least two receiver antennas and one transmit antenna; (c) having a maximum transmit power of 23 dBm.
3GPP LTE Rel-12 has defined a UE power saving mode allowing long battery lifetime, and a new UE category allowing reduced modem complexity. In Rel-13, further MTC work is expected to further reduce UE cost and provide coverage enhancement. The key element to enable cost reduction is to introduce reduced UE Radio Frequency (RF) bandwidth of 1.4 Mega Hertz (MHz) in the DL and the UL within any system bandwidth.
Channel Quality Indicator (CQI)
CQI may be understood as information signalled by a UE to the base station to indicate a suitable data rate, typically, a Modulation and Coding Scheme (MCS) value, for DL transmissions, usually based on a measurement of the received DL Signal to Interference plus Noise Ratio (SINR) and knowledge of the UE's receiver characteristics. The CQI indices and their interpretations are given in Table 7.2.3-1 of 3GPP TS 36.213 V12.4.0 for reporting CQI based on Quadrature Phase Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (QAM) and 64QAM.
Table 1 depicts an example of an existing 4-bit CQI Table, as described in 3GPP TS36.213 V12.4.0, Table 7.2.3-1. Table 1 comprises a number of entries or rows. Each entry has assigned an identifier, the CQI index, which is a number from 0-15 in this case. Each entry is associated with a respective value of modulation, e.g., QPSK, 16QAM or 64 QAM. Each entry is also associated with a respective value of code rate and efficiency. In Table 1, the code rate ×1024 indicates a quantized version of the code rate. Also in the table, the efficiency indicates the number of information bits that may be sent per modulation symbol. Out of range, in Table 1, indicates that the radio node, e.g., the eNodeB, may not reliably transmit a transport block to the UE, even with the lowest modulation and coding rate scheme, i.e., the CQI index 1 does not satisfy the condition of transport block error probability not exceeding 0.1 when the PDSCH uses the corresponding combination of modulation scheme and transport block size.
Based on an unrestricted observation interval in time and frequency, the UE may derive, for each CQI value reported in UL subframe n, the highest CQI index between 1 and 15 in Table 7.2.3-1, or Table 7.2.3-2, which satisfies the following condition, or CQI index 0 if CQI index 1 does not satisfy the condition:                A single Physical Downlink Share Channel (PDSCH) transport block with a combination of modulation scheme and transport block size corresponding to the CQI index, and occupying a group of DL physical resource blocks termed the Channel State Information (CSI) reference resource, could be received with a transport block error probability not exceeding 0.1.        
TABLE 1codeCQIrate ×indexmodulation1024efficiency0out of range1QPSK780.15232QPSK1200.23443QPSK1930.3774QPSK3080.60165QPSK4490.8776QPSK6021.1758716QAM3781.4766816QAM4901.9141916QAM6162.40631064QAM4662.73051164QAM5673.32231264QAM6663.90231364QAM7724.52341464QAM8735.11521564QAM9485.5547
The existing CQI table may not be applied to MTC, since the existing CQI table assumes that a PDSCH transmission is contained within a single subframe. This does not work for low-complexity and/or enhanced coverage MTC UEs, because they may rely on repetitions of data transmission, which may extend beyond a single subframe. The existing CQI table assumes that one PDSCH transmission carries one transport block. In MTC, the numerous repetitions of a single PDSCH, together may carry a single TB. The number of repetitions of the PDSCH may be tens of repetitions or hundreds of repetitions, depending on the level of degraded channel quality the UE experiences. Ignoring the availability of the PDSCH repetitions may lead to the UE indicating lower CQI index than necessary. For example, down to a certain degraded chancel quality, using the existing CQI table may lead to the UE indicating “out of range” to eNodeB, causing the eNodeB to not scheduling any PDSCH transport block to the UE. Therefore, applying the existing CQI table to MTC may severely bias the PDSCH transport block transmission to a low modulation and coding scheme corresponding to a low CQI, including no scheduled transmission opportunity, leading to a reduced performance of the wireless communication network.
Further detailed information on the subjects just exposed may be found for example, in 3GPP TS 36.211 V12.0.0, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 12), 3GPP TS 36.213 V12.4.0, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 12), and 3GPP TR 36.888 v12.0.0, Study on provision of low-cost Machine-Type Communications (MTC) User Equipments (UEs) based on LTE (Release 12).